As a video image formation device, a projection display displaying video images on a screen has been widely spread. For a projection display, a lamp light source is generally employed. However, a lamp light source has drawbacks in that the lifetime is short, the light utilization efficiency is low, and the color reproduction range is limited.
In order to solve these problems, it is attempted to employ a laser light source as a light source for a picture formation device. The laser light source is lengthy in its lifetime with relative to a lamp, and further, since it has strong directionality, it is likely to enhance the utilization efficiency. Further, since the laser light source shows the monochromaticity, the color display range is large and the display of vivid image is possible.
A schematic view of a laser picture formation device is shown in FIG. 12. The lights emitted from the laser light sources 1R, 1G, and 1B of RGB three colors are introduced to the illumination optical system 2 which irradiates the modulation element 71. The illumination optical system 2, which includes speckle noise removal means 3, optical integrator 4, and projection optical system 6, shapes the light beam from the laser light source into the same configuration as the effective plane of the modulation element 71 as well as makes its light intensity distribution uniform, thereby irradiating the modulation element 71. After video images are modulated by the modulation elements of respective colors, the lights are synthesized by the dichroic prism 9, and the resulted color image is broadened and projected onto the screen 10 by the projection optical system 8. The speckle removal means 3, which comprises such as a rotating renticular lens, varies such as an angle of the laser light in view of time, thereby removing speckle noises which occur due to the interferences of laser lights.
As described above, in a display employing a laser light source (hereinafter, referred to as a laser display), there is a problem that speckle noises may occur due to that the laser lights have high coherency. The speckle noises are noises in minute particle like shapes which can be captured by viewer's eyes due to that the scattered lights interfere with each other when the laser lights are scattered by the screen. The speckle noises are noises which are produced by particles having sizes which are determined by the F (F number) of the viewer's eyes and the wavelength of the laser light source are arranged at random, and these obstruct the observer from capturing the video images on the screen, thereby leading to a serious deterioration in video images. Particularly, the speckle noises due to the lasers of the wavelengths of green and yellowish green which have high visibility to human beings cause large influences in the video image deterioration.
Up until now, as a method for reducing the speckle noises, there was such as a proposal of deflecting the light with a frequency that is higher than the frame frequency in a spatial modulator and irradiating the resulted light to the spatial modulator, thereby to reduce speckle noises (for example, Patent Document 1).
In addition, in a laser picture formation device employing RGB light emission elements, there was a proposal of employing an array of RGB light emission elements and employing a single modulation element in a time divisional manner (for example, Patent Document 2).    Patent Document 1: Japanese Published Patent Application No. 10-293268    Patent document 2: Japanese Published Patent Application No. 2001-249400